Chemical-mechanical polishing is one technique utilized to process the outer surface of various layers formed over a semiconductor wafer. One principal use of chemical-mechanical polishing is to render an outer wafer surface of a layer or layers to be more planar than existed prior to starting the polishing. Only some or all of the outermost layer being polished might be removed during such a process.
In chemical-mechanical polishing, both the wafer and the pad which polishes the wafer are typically caused to rotate, typically in opposite directions, during the polishing action. A liquid slurry is received intermediate the wafer and the polishing pad. The slurry comprises a liquid solution, typically basic, and a solid grit material, typically constituting particles of a consistent size (i.e., within 5 nanometers of a size selected from around 25 to 100 nanometers in diameter). The action of the liquid solution and grit within the slurry intermediate the wafer and pad imparts removal of outer wafer layers utilizing both chemical and mechanical actions.
Semiconductor wafer processing continues to strive for ever increasing miniaturization and circuit density. Consequently, the separation distance between circuit components needing to be electrically isolated continues to shrink. For example, fabrication of integrated circuitry typically involves forming electrically isolated active areas from the semiconductive material of the wafer. The isolation is achieved by forming insulating isolation regions between discrete active areas. The isolation regions are typically formed from an oxide material which is either grown or deposited over the wafer. In the recent past, a technique referred to as shallow trench isolation has emerged as one way of providing isolation regions for the ever decreasing geometries. Here, a series of shallow trenches (i.e., one micron or less in depth) are formed within a substrate by patterning and etching. The trenches are subsequently filled with an oxide material, most typically deposited by a high density plasma deposition. The oxide is subsequently planarized by chemical-mechanical polishing, for example as described above. This forms discrete active area regions separated by isolation oxide.
As the separation between active areas fell to and below 0.3 micron, ever increasing and unacceptable circuit failures were discovered. This of course reduces yield and accordingly requires discarding of an increasing volume of potentially salable product.